SJA WILLIAM SIEMENS, F.R.S. 323 



vacuum so as to attain the advantage of using the steam 

 repeatedly, he might add that many years ago he proposed to 

 evaporate liquid cane juice by pumping the steam from the 

 vacuum pan, which was in the form of a locomotive boiler, into 

 tubes surrounded by liquid in order that it might be condensed 

 there. To sustain the further evaporation of the same liquid, a 

 steam engine and pumping cylinder were employed, whereby the 

 steam generated within the evaporating pan at about half the 

 pressure of the atmosphere was compressed, and forced into the 

 tubes at double, or atmosphere pressure. Its condensing point 

 was raised in compression from 180 to 212, which difference 

 sufficed to cause the recondensation of the steam within the tubes 

 and a continued ebullition of the juice, the same latent heat being 

 made to serve over and over again. The only real expenditure in 

 this operation was mechanical force, but the steam employed in 

 generating this force was necessarily much less in amount than 

 the steam compressed by it through half an atmosphere. More- 

 over, the exhaust steam of the engine was made available to make 

 up for the loss by radiation, and for bringing the cold juice up to 

 the boiling point. 



Such a process could not fail to work practically, but the 

 mechanism involved in it was of a nature to make its application 

 costly. The project was revived last year by Mr. Robertson, who 

 after hearing the Paper on " Pneumatic Despatch Tubes ; the 

 Circuit System," by Mr. Carl Siemens, M. Inst. C.E.,* conceived 

 that the steam blast apparatus referred to, being capable of 

 maintaining a vacuum of 20 inches of mercury, could be made to 

 serve also to force the vapour raised in a vacuum pan into the 

 evaporating tubes of the same or another pan, and thus to 

 combine the advantage of evaporating the juice under a reduced 

 pressure with that of repeatedly using the latent heat of the 

 steam. Mr. C. W. Siemens considered this plan to be superior 

 to that originally proposed by himself, inasmuch as the apparatus 

 employed was simple and inexpensive. When tried in London, 

 Mr. Robertson found that a vacuum of 20 inches could be main- 

 tained in his vacuum pan. In that case, as in the former, the 

 steam employed in compressing the vapour in order to fit it for 



* Vide Minutes of Proceedings of the Institution of Civil Engineer!, VoL 

 XXXIII., p. 1. 



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